elka 103 – Bulgarian pocket calculator

My site has already featured material about calculators from the USSR and Japan, but I have never prepared a description of a device from Bulgaria. It’s time to change that. 

Marking elka 103 with a beautiful typeface

In most of the former Eastern Bloc countries, the idea of producing their own calculating machines, or calculators, came up at some point. The same was true in Bulgaria, or rather in the People’s Republic of Bulgaria, as that was the country’s official name from 1946 to 1990.The first prototypes developed by the Central Institute of Computing Technology are created in the mid-1960s and produced by the Elektronika (електроника) plant located in the capital Sofia. The first series of devices was named “ELKA,” an abbreviation of ЕЛ (ектронен) КА (лкулатор) , meaning “electronic calculator.” Over time, the word elka became a generic name for calculators produced in Bulgaria.

The first mass-produced model was the Elka 6521. This rather large calculator, weighing as much as 16kg, supported, among other things, the square root function. On the Internet you can come across an opinion that it was the first device with such functionality, but this is not true. Bulgarian engineers Petar Popov and Stefan Angelov were preceded by developers from the states. Nevertheless, the Balkan duo was honored with the highest decoration in socialist Bulgaria – the Order of Georgia Dimitrov.

elka 103

The hero of today’s material is the younger brother of the Elka 6521 calculator with the designation 103. The design of this model began in 1973, and it went into production two years later in 1975. The Elka 103 belongs to a larger family of 100-series devices, produced primarily for export to other Eastern Bloc countries. 

The calculator has a small size, also without hesitation we can describe it as pocket-sized. The case is made of two plastic parts in different colors. The front panel, if we can call it that, is black in color and has a slightly rough texture, the bulk of it is occupied by a twenty-key keyboard. The keys are plastic and have a rather large stroke, other than that they are not very precise and it happens that a single press will generate several of the same digits. Above the keyboard is a metal plate with a cutout for the on/off switch and a translucent red panel protecting the display.

The Elka 103 is a basic calculator, supporting six mathematical operations, but it is noteworthy that the device is equipped with a memory.

bottom of the calculator

The back of the calculator was made of really nice-looking orange plastic. The elka 100 series devices could come in three color versions – orange, yellow and green. With the 103 model itself appearing only in orange (version one) and yellow (version two) I was unable to find any photos of the elka 103 in green. 

On the bottom of the device there was a battery cage flap, four rubber feet and two screws, which were originally obscured by the nameplate, but unfortunately there is none in my copy.

The sticker, a photo of which I found on the Internet, included information about the model, exporter, power supply and country of origin.

Battery cage

Under the flap there was room for four AA batteries to power the device. Interestingly, there was also a fabric ribbon, which, placed under the batteries, will make it easier to remove them later. I have so far encountered such a solution only in Sharp’s Japanese calculators. In the place for the batteries there are two additional screws holding the case together. 

What is hidden inside?

Device in two parts

After removing four screws, we can disassemble the calculator into two parts – the front part with the keyboard and display, and the back part with the batteries and main board. Both parts are connected to each other by a bundle of wires.

Keyboard design

The design of the keyboard was based on a PCB, it is the PCB that forms its backbone. On the same laminate the display has been placed. The board is connected to the plastic housing thanks to two pillars visible on the left side. Unscrewing them, we can get inside the keyboard, but this should be done carefully, so that the plastic buttons do not fall out of their places.

A part of the keyboard that is not visible on a daily basis

The operation of the buttons was based on metal plates, soldered to the PCB. When you push the button, you press on the metal plate, which forms an electrical connection between the field on the laminate and itself.

Switch located on the PCB

There are also two areas on the board that together with a movable switch form a structure that allows the calculator to be turned on. Moving the switch connects or disconnects the connection between the two areas on the PCB.

Push buttons

The physical buttons have been integrated into the calculator’s case and work on the principle of small levers that always return to their place. We can also see a movable switch. Since the devices in the elka 100 series shared the same housing, there were two additional holes above the switch, where other switches were placed, obviously in higher models.


The display is a classic design for calculators originating from a centrally planned economy. It is composed of nine digits, each with 7 segments, while a single segment itself consists of three luminous structures. Despite such a large number of segments, the display has relatively few leads. This is because a single bus is used for control, so the display must be multiplexed. 

Displays of this type were also manufactured in Poland by the CEMI plant. Our native design was designated as CQYP95. However, this copy probably came from Czechoslovakia, since it was the displays from that country that had the black laminate. 

Display while the calculator is running
The second part of the housing

Now let’s return to the second part of the elka 103’s case. Most of it is occupied by the battery cage, but the motherboard and the socket for an external power supply were also located here.


The main board is quite small and consists of few components. Here we have, 6 transistors, 4 diodes, 17 resistors and 5 capacitors. However, what catches the eye are the two largest components, a black cuboid that is a transformer labeled TP024 and the main A5502CB processor. 

Not much is known about the A5502CB chip. Its manufacturer is Rockwell International company, which was dissolved into several smaller companies in 2001, besides, from the 7648 designation we can deduce that the design was produced 48 week 1976. The chip was also used in another Bulgarian calculator – elka 130, by which we know that today’s hero does not use the full capabilities of the chip. The elka 130 was a higher model supporting more computing functions. Interestingly, both the 103 and 130 may also have been based on a slightly different A5502PB chip, probably an improved version of the A5502CB with identical functionality.  

Bottom of the motherboard

On the bottom of the motherboard you will not find any components, there are only very nicely routed paths here.

How to make an elka 103 into an elka 130?

Modification Source: http://www.calcuseum.com/SCRAPBOOK/BITMAP/BONUS/18514/_SMD311806_XL.htm

As I mentioned, the elka 103 and the elka 130 are quite similar designs based on the same chip, except that the 130 model took full advantage of the power inherent in the processor. The question can then be asked, can the capabilities of the 103 model be increased? It turns out that yes. To do so, you need to add three jumpers on the keyboard board. The author of the modification experimented on the second version of the elka 103 in the yellow-black case, whose keyboard PCB differs from my copy, so not wanting to damage the calculator, I did not carry out this type of modification on mine.  


  • https://en.wikipedia.org/wiki/ELKA
  • https://vintage-technology.club/pages/calculators/e/elka103o.htm
  • https://www.vintage-technology.club/pages/calculators/e/elka103y.htm
  • https://www.flickr.com/photos/wisbey/319080147
  • https://www.calculator.org/calculators/Elka_103.html
  • http://www.calcuseum.com/SCRAPBOOK/BONUS/33495/1.htm
  • http://www.calcuseum.com/SCRAPBOOK/BONUS/18514/1.htm
  • https://en.wikipedia.org/wiki/Rockwell_International

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